Since the advent of "high fidelity" audio systems, engineers have strived to develop loudspeakers that were relatively free from distortion and with a frequency response that would allow concert hall music to be closely reproduced. Loudspeakers are broadly categorized as being either magnetic, moving coil speakers or non-magnetic, electrostatic speakers/transducers. The instant invention discloses an electrolytic speaker which is more closely related to the electrostatic types. Therefore, the reminder of the discussion pertains to only electrostatic speakers.
Most prior art electrostatic speakers generally consist of a center flexible membrane or diaphragm having on each side a fixed electrode in the form of a grid of wires. The wires are spaced apart so as to enable sound waves generated by the movement of the flexible membrane to be emitted. The wires are sheathed in a dielectric insulation material and the flexible membrane has a coating of a highly resistive material. The membrane is further suspended within an open latticed frame between the electrode wires so that when operated, relatively small segments of the diaphragm are enabled to vibrate under the influence of the electrostatic fields acting upon the diaphragm.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention however, the following U.S. patents were considered related:
______________________________________ U.S. Pat. No. INVENTOR ISSUED ______________________________________ 4,160,882 Driver 10 July 1979 3,942,029 Kawakami et al 2 March 1976 3,705,312 Sessler et al 5 December 1972 3,345,469 Rod 3 October 1967 ______________________________________
The Driver patent discloses an electrostatic transducer that has applicability as a loudspeaker. The transducer consists of two parallel diaphragms each consisting of two plastic sheets, having different charge carrying characteristics, that are sandwiched between an electrically conductive layer. The two diaphragms are separated by a centrally located perforated electrically conductive sheet and a dielectric material sandwiched between the conductive sheet and each diaphragm. The diaphragm's two electrically conductive layers are connected across the secondary winding of an audio transformer and the centered electrically conductive sheet is connected to the center tap of the transformer. Thus, when the transformer is applied an audio signal the two diaphragms are driven in a push-pull relation to reproduce the audio.
The inventor of the U.S. Pat. No. 4,160,882 is also the inventor of the instant application and pending application Ser. No. 07/949,801. The instant application differs from both the patent and the pending application in that the transducer driver unit has been redesigned and the improved electrolytic loadspeaker assembly no longer requires polarization or a bias regulator/dielectric drain circuit.
The Kawakami et al patent discloses an electrostatic transducer that can be utilized in either a speaker or microphone. The transducer consists of a vibrating plate or electret diaphragm having a monocharge of positive or negative potential on its surface. The electret diaphragm is made of a thin polymer film that is bonded to a support so that uniform tension exists. A pair of electrically conductive electrodes are brought in contact with opposite sides of the polymer films, and an electrostatic shield, such as a mesh, covers the surface of the two electrodes. A d-c voltage is time-applied across the electrodes to allow the electret to heat to its curie temperature of 120.degree. C. The electret is subsequently cooled to produce a quasi permanent state of electric polarization.
The Sessler patent discloses a method for preparing a thin-film electret. The method includes placing a thin polymer film between two electrodes together with a dielectric plate. A voltage of about 30 keV is then applied across the resulting sandwich of elements for about one minute at room temperature and at atmospheric pressure. The method produces charge-densities which are greater by a factor of three than those previously reported.
The Rod patent discloses a loudspeaker that operates on electrostatic principles. The speaker consists of a centrally located movable diaphragm which is coated on both sides with a thin, flexible electrically conductive layer. On each side of the diaphragm is located at least one hermetically sealed plastic dielectric sheet. When air or other gas is trapped between the sheets and the diaphragm, a buffer zone is created. To each outermost dielectric sheet is attached an electrode and to the centered conductive diaphragm is likewise attached an electrode. The two buffer electrodes are connected across the secondary winding of a step-up transformer and the diaphragm electrode is connected through a d-c voltage source to the centertap of the transformer. The transformer's primary winding is connected to the diaphragm driving signal that is derived from the signal input from a conventional low-impedance amplifier.
The above described electrostatic transducers, although being superior in many respects over the moving-coil type, have received poor industry/consumer acceptance. This poor acceptance is due in part to the undue mechanical complexity of some designs, low acoustic output, the requirement for a comparatively large radiating area and a dependence upon the application of a relatively high d-c polarizing bias voltage between the flexible diaphragm and the wire grid electrodes. For example, a typical full range push-pull electrostatic speaker requires a bias voltage of 3500 volts d-c and a driving amplifier with a power capacity of from 60 to 100 watts. Additionally, the prior art electrostatic speakers are only able to reproduce adequately from the mid-range and higher audible frequencies. Therefore, a bass speaker is commonly connected to reproduce the bass frequencies.
To overcome some of the above defects, transducers utilizing electrets as the diaphragm have been employed. The electret diaphragm was thought to be permanently polarized or charged and therefore not requiring a separate polarizing d-c voltage. However, these electrets have been found to be unsatisfactory for application as loudspeakers because they decay, at least to a first approximation, according to an equation of the form dp/dt=oc P because the misalignment of the partially oriented dipoles is a random process.
For background purposes and as indicative of the art to which the invention relates, reference may be made to the following remaining patents found in the
______________________________________ PATENT NO. INVENTOR ISSUED ______________________________________ 4,726,443 Ugaji, et al 23 February 1988 3,941,946 Kawakami et al 2 March 1976 2,037,537 (GB) Kawasaki 9 July 1980 ______________________________________